Rotary wing aircraft and tiltrotor aircraft are difficult to store due to the span covered by the relatively large rotors thereon. The problem has become particularly acute with the use of multi-rotor helicopters and with the advent of tiltrotor aircraft where the rotors are carried at the very tips of the wing. A large amount of space is required to store such aircraft and in some instances, such as on aircraft carriers, the space required for storing such aircraft with the rotors extended or deployed is not available.
With the early rotary wing aircraft, if folding was necessary, manual manipulation of the blades and lock pins retaining the blades was adequate. However, with larger aircraft and particularly with the tiltrotor aircraft where the blades are located very high and at the tips of the wing, power folding has become a virtual necessity.
U.S. Pat. No. 3,625,631 issued to Cecil E. Covington, et al. on Dec. 7, 1971. That patent describes a system for positioning pairs of rotor blades so that they are aligned parallel to the centerline of the fuselage. Since there are no wings on the aircraft, folding the rotor blades in this manner reduces the required storage area essentially to the width and length of the fuselage.
U.S. Pat. No. 3,749,515 issued July 31, 1973 to Cecil Covington, et al. The powered blade folding mechanism described in that patent, does fold one rotary blade relative to the other. Also, during the folding process a locking pin is withdrawn and reinserted automatically so that the blade will be locked in position when deployed.
It is contemplated in U.S. Pat. No. 3,749,515 that such power folding mechanism would be utilized on convert-a-planes so that the blades could be folded to reduce drag during level flight. In that type of aircraft, a separate propeller or propulsion means is utilized during horizontal flight so that the rotor blades are not used for this purpose. With the advent of the tiltrotor aircraft, the same power plant and same rotor blades are utilized for both horizontal and vertical flight. To convert from vertical flight to horizontal flight, the tiltrotors are rotated relative to the aircraft so that the rotors are oriented with the blades in the proper attitude to provide horizontal flight. To reduce the drag on the aircraft during horizontal flight, it is desirable to provide fairings over the rotor drive hub and over the connections between the blades and the rotor hubs. In the tiltrotor aircraft, it is virtually mandatory that such blades be arranged to be power folded if storage space is a consideration.
In order to power fold the blades of faired rotors, it is necessary to not only provide a lock which is automatically withdrawn before folding and which is reinserted after the blade is deployed, but it is also necessary to provide for the removal of a portion of the fairing or fairing door in the direction in which the blade is folded. It is also necessary that such fairing door be securely latched when the blade is deployed.
An additional problem, when the rotors are used in level flight, is that the blades need to be of an adjustable pitchtype. To control the position of the blades when folded and during storing on the tiltrotor-type aircraft, it is necessary that a lock be provided to prevent an inadvertent change in pitch angle.
Accordingly, an object of this invention is to provide an improved apparatus and method for power folding rotor blades that are of the variable pitch-type.